Spectral beam combining is an effective method to increase the total output power of a laser system while maintaining ahigh beam quality. The diffraction grating with high diffraction efficiency and high laser damage threshold is the keycomponent in a spectral-beam-combining laser system. To meet the above requirements, we design a grating on top of ahigh-reflectivity HfO2/SiO2 thin-film stack. The diffraction efficiency of the grating depends mainly on the duty cycleand depth of the grating grooves. The grating was fabricated by using optical interference lithography and reactive ionbeam etching. To achieve high efficiency, we controlled the duty cycle by applying an end-point detection techniqueduring development and we controlled the groove depth by adjusting the ion-beam etching time length. In a 50 mm × 50mm fabricated grating area, the measured diffraction efficiency in TE polarization was 95.8 ± 1.1 % at the centerwavelength of 1030 nm. In the wavelength range of 1025 nm to 1035 nm, the measured average diffraction efficiency inTE polarization was 97.7% at center of the grating sample. We describe the details of our work, including designparameters, fabrication processes, and measured diffraction efficiencies.
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